The present invention relates to a process and apparatus for forming a bias seam, and more specifically, to a process and apparatus for forming a bias seam using an ultrasonic sealing apparatus.
Bias binding containing a bias seam, or a seam on the bias, is generally used to bind edges or cover seams to give a product a finished look. The bias binding is arranged such that the threads or yarns of the fabric run on an angle from the edge rather than parallel or perpendicular to the edge. This permits the binding to have some elasticity or stretch enabling the binding to go around curves or comers and lay flat without puckering. A straight binding, i.e., not on the bias, would appear unappealing if sewn other than in a straight line as it would pucker when sewn around curves.
To prevent fraying of the edges. the edges to be sewn together are folded under to produce a "clean finish." An apparatus for folding the binding edges is attached to the sewing machine. The apparatus folds each edge and guides it to the needle. The presently used sewn bias binding thus has two butterfly edges on the reverse side of the seam. The two-ply butterfly edges create bulk which can have difficulty passing through finishing attachments. In addition, the sewn seam has holes from the sewing needle and spaces between the stitches regardless of how close they are together. Hence, the seam is subject to leakage.
The folding apparatus described above is capable of accommodating single bindings and multiple bindings. When the seams of the bindings are passed through the folding apparatus, the butterflies on the back of the seam, especially with multiple bindings, cause considerable friction in the folding apparatus, which results in inconsistent feeding, irregular stitches and defects. Still further, there are times when the butterflies are caused to be turned back at the entrance of the folding apparatus resulting in three-ply bulk, thereby making the problem of friction even worse.
Sewn bias seams also have a tendency to pull apart slightly at the edges as it is impossible to lock either the first stitch or the last stitch.
Ultrasonic bonding is a well-known process in which high frequency vibrations are imparted into two or more plies of a thermoplastic material with a horn. The horn vibrates adjacent to an anvil which supports the material. The vibrations develop frictional heat at the seam interface, subsequently bonding the material together. Materials may also be cut or slit with an ultrasonic horn while sealing the edges. The ultrasonic horn couples mechanical vibrations into the material, while the anvil supports the material during the sealing process.
A review of the ultrasonic binding art indicates a need for a process of and an apparatus for forming a bias seam using an ultrasonic sealing apparatus.
U.S. Pat. No. 3,666,599 to Obeda describes an ultrasonic seaming apparatus in which the feed rate of the workpiece through the seaming station and the velocity of the resonator are interconnected in such a manner that both are varied in a predetermined relationship.
U.S. Pat. No. 3,852,144 to Parry describes an ultrasonic seaming and cutting apparatus having a resonant horn, a rotating anvil wheel and a cutting surface disposed in juxtaposition with the anvil wheel. The apparatus is adapted to simultaneously cut and fuse the material adjacent the seamed area without excessive wear in the instrumentality providing such cutting action.
U.S. Pat. No. 4,333,791 to Onishi describes an ultrasonic seam welding apparatus for seam welding at least two sheet-like work pieces piled one above the other. The seam welding is carried out by imparting the ultrasonic oscillation to the workpieces from the converter-horn assembly with the aid of the roller.
U.S. Pat. No. 4,373,982 to Kreager et al. describes an ultrasonic sealing apparatus where plastic film in sheet form is supplied to a forming unit which forms the plastic film into tubular form with overlapping edges. The edges are caused to pass along an anvil and the horn of an ultrasonic sealing unit for effecting ultrasonic sealing of the edges. The edges of the film are passed through a gap between the horn and the anvil.
A publication by Sonobond Ultrasonics Company titled "Ultrasonic Techniques for Thermoplastic Fabrics and Apparel" describes the ultrasonic sealing process in connection with thermoplastic fabrics and apparel. Under Cut and Seal Edge Finishing, the company describes sealing of the ends of a bias tape to prevent raveling using an ultrasonic apparatus. This process is unrelated to forming a bias seam.
For details concerning the design and construction of the ultrasonic sealing apparatus, reference is made to the book entitled "Ultrasonic Engineering" by Julian R. Frederick, John Wiley & Sons, Inc., New York, N.Y. (1965).
All patents and publications cited in the specification are herein incorporated by reference.